Field of the Invention
The present invention relates to a workpiece conveying apparatus (workpiece conveying robot) for a pressing machine (press machine)
Background
Hitherto, there have been proposed various workpiece conveying apparatus configured to carry workpieces into and out of a press machine, or carry workpieces between the press machines.
For example, in Japanese Patent Application Laid-open No. 2009-95940, there is disclosed a workpiece conveying robot including, as illustrated in FIG. 17, a first arm that is horizontally rotatable, a second arm that is supported at a distal end of the first arm so as to be rotatable about an axis that is parallel to a rotation axis of the first arm, a flange that is arranged at a distal end portion of the second arm so as to be rotatable about an axis that is parallel to a rotation axis of the second arm, a workpiece holding portion provided to the flange, and a speed reduction mechanism having at least two output axes at the axis parallel to the rotation axis of the first arm.
In this context, during workpiece conveyance using the workpiece conveying robot as described above, workpiece holding means (workpiece holding portion) is moved to a predetermined position in a preceding step, specifically, a predetermined position in a lower die of a pressing machine, while avoiding interference with a slide that vertically moves (upper die). At the predetermined position, a moving-down operation (lowering operation) is performed so that the workpiece holding means comes close to and holds a workpiece. After the workpiece holding means holds the workpiece, a moving-up operation (raising operation) is performed, and the workpiece is taken out of the predetermined position in an upstream step (predetermined position in the lower die). Then, the workpiece holding means is moved to a predetermined position in a subsequent step, specifically, a predetermined position in a lower die of another pressing machine. At the predetermined position, the moving-down operation (lowering operation) is performed, and the workpiece is released. After the workpiece is released, the moving-up operation (raising operation) is performed, and the workpiece holding means is returned to the predetermined position in the preceding step. In this way, workpiece conveying operations are performed.
Thus, in the workpiece conveying robot described in Japanese Patent Application Laid-open No. 2009-95940, a ball screw is used so as to cause a swivel base, which supports the first arm so that the first arm is horizontally rotatable, to vertically move with respect to a base. With this, the workpiece holding means (workpiece holding portion) is vertically moved during the workpiece conveyance.
However, weight of a workpiece conveying robot to be used for conveying workpieces between generally assumed pressing machines such as pressing machines for automobile bodies is approximately two tons or more. Thus, as described in Japanese Patent Application Laid-open No. 2009-95940, in order to vertically move the entire workpiece conveying robot, in other words, all the arms by using the ball screw, vertical drive mechanisms having a high capacity and a high rigidity (including their drive sources) are needed. As a result, cost may be increased.
Further, in such a system, the workpiece conveying robot having great weight is vertically moved overall, and hence intense vibration and noise are generated. In addition, a rigidity of frames configured to support the workpiece conveying robot needs to be increased as a matter of course, and distal ends of the arms are unnecessarily intensely vibrated. In this way, in terms of practicality, such a system is not suited to high-speed workpiece conveyance.
Still further, in the workpiece conveying robot described in Japanese Patent Application Laid-open No. 2009-95940, it is desired that postures of the workpiece and the second arm, which are fixed within a horizontal plane, be changed, specifically, postures be inclined in directions other than the horizontal direction as far as interference with the upper die that vertically moves does not occur so as to increase a workpiece conveying speed as much as possible.